This invention relates to a method for enhancing the crystallization rate of thermoplastic butene-1 polymer compositions. More particularly, this invention is directed to the addition to a butene-1 polymer composition of small amounts of certain amides as nucleating agents, thereby promoting the crystallization of the polymer from the melt and affording compositions which exhibit improved properties, compared to the non-nucleated butene-1 base polymer composition.
Heterogeneous nucleation via the addition of a foreign material or nucleating agent is well known. See, for example, Chatterjee et al., J. Polym. Sci.; Polym. Phys. Ed., Vol. 13, 2369-83 and 2385-90 (1975). As demonstrated therein, heterogeneous nucleation is highly selective and there is no evidence of a universally strong nucleating agent for all polymers. In other words, an effective nucleating agent for one polymer may be ineffective for even a closely related polymer; similarly, even a compound closely related to an effective nucleating agent for one polymer may be ineffective for that same polymer. Chatterjee et al. also disclosed the use of nylons (polyamides) as nucleating agents for polypropylene crystallization. Nucleation and specific nucleating agents are discussed in Binsbergen, J. Polym, Sci.; Polym. Symposium, Vol. 59, 11-29 (1977).
The use of a nucleating agent to accelerate the crystallization of polymers allows for faster processing and results in a more uniform microstructure because of the reduced size of the spherulites which form upon melt crystallization. The products also generally demonstrate improved physical and mechanical properties. See, for example, Rubin, Injection Molding Theory and Practice, pp. 192ff (1972). In general, a desirable nucleating agent is effective at low levels of addition, both for reasons of economy and the avoidance of undue foreign structural heterogeneity which may otherwise adversely affect the properties of the polymer. It has now been discovered that certain amides are highly effective nucleating agents, at low levels of addition, for butene-1 homopolymers and copolymers with ethylene.
Various additives for polyolefins are disclosed in U.S. Pat. Nos. 3,902,532 (higher fatty acid amide slip agents), 3,499,884 (nylon salts), 3,440,168 (nylon fibers) and 3,268,499 (lithium salts of isonicotinic acid and p-acetamido benzoic acid).
Belgian Pat. No. 695,803 and U.S. Pat. No. 3,756,997 disclose a variety of nucleating agents for butene-1 polymers. Specific examples include polypropylene, coumarone-indene resin, aluminum silicate, clay and aromatic sulfonic acids and their derivatives, including 4-amino benzene/sulfonic amide. Certain fatty acid amides are disclosed as nucleating agents for butene-1 polymers in my co-pending application Ser. No. 216,055, filed Dec. 15, 1980.